I'll try my best to answer your questions.
For placing the tricks, when it says that another trick won't fit, move the other tricks over the side or something, then the other trick should fit. Then you can put the tricks back to wherever you want them. I'm not sure why it won't let you add another animal. Have you trained the other animals? Did you go into the tab and select another animal? It might just be a weird glitch, too.
For the elevated paths, try changing your view while building the paths, and it may make it easier to build them more symetrical.
The cheats that you found are for Zoo Tycoon 1. At least most of them are. You can't name an exhibit for ZT2.
I hope I helped. ![Smile [:)]](/emoticons/emotion-1.gif)

Thanks Firesong for the awesome sig!